A large number of nipples for use on an infant bottle have been proposed heretofore. For relevant prior art, see U.S. Pat. Nos. 3,651,973; 3,648,873 and 3,358,864. The devices disclosed in said patents require special considerations, special construction for venting air, or a special device for collapsing the liner containing the liquid by contact with the liner. The present invention solves the problem of removing air from within the collapsible liner in a manner which is simple, inexpensive and reliable.